This invention relates to heat exchangers, and in particular, to bypass valves for bypassing or short-circuiting flow from the heat exchanger inlet to the heat exchanger outlet under conditions where the heat transfer function of the heat exchanger is not required or is only intermittently required.
In certain applications, such as in the automotive industry, heat exchangers are used to cool or heat certain fluids, such as engine oil or transmission fluid or oil. In the case of transmission fluid, for instance, a heat exchanger is usually used to cool the transmission fluid. The heat exchanger is usually located remote from the transmission and receives hot transmission fluid from the transmission through supply tubing, cools it, and delivers it back to the transmission again through return tubing. However, when the transmission is cold, such as at start-up conditions, the transmission oil is very viscous and does not flow easily through the heat exchanger, if at all. In such cases, the transmission can be starved of fluid and this may cause damage to the transmission or at least erratic performance. Damage can also be caused to the transmission if the quantity of fluid returned is adequate, but is over-cooled by the heat exchanger due to low ambient temperatures. In this case, water may accumulate in the transmission fluid as a result of condensation (which normally would be vaporized at higher temperatures) and this may cause corrosion damage or transmission fluid degradation.
In order to overcome the cold flow starvation problem, it has been proposed to insert a bypass valve between the supply and return tubing to and from the heat exchanger. This bypass valve may be temperature responsive so that it opens causing bypass flow when the transmission fluid is cold, and it closes to prevent bypass flow when the transmission fluid heats up to operating temperature An example of such a bypass valve is shown in U.S. Pat. No. 6,253,837 issued to Thomas F. Seiler et al. While this approach works satisfactorily, the heat exchanger and bypass valve assembly becomes quite large and includes fluid inlet and outlet tubing that may not otherwise be required.
In the present invention, the bypass valve can be incorporated as an integral part of the heat exchanger as a plug-in item that can be located anywhere desired between the inlet and outlet flow manifolds of the heat exchanger.